In our overall goal to understand the cellular mechanisms involved in glucose-induced insulin release we have developed biochemical procedures for isolating an endoplasmic reticulum (ER) enriched fraction obtained from islet cells. We have characterized this fraction for purity and identified both passive and ATP-dependent Ca++ uptake by this subcellular organelle. ATP-dependent Ca++ transport and Ca++ stimulated ATPase activity localized to the ER have been distinguished from that associated with an islet-cell plasma membrane enriched fraction. In this project we will use islet-cell ER model to study intracellular Ca++ metabolism by determining the regulatory role of physiological factors i.e., insulin secretagogues, inhibitors, cystolic components, and the secretory state of the islet to modulate passive and ATP-dependent Ca++ uptake. Ca++ efflux from ER vesicles preloaded with Ca++ will be studied to determine the effect of insulin secretagogues and other agents on the efflux of Ca++ from this organelle. A Ca++ stimulated ATPase activity will be characterized to determine if a correlation exists between the Ca++ stimulated ATPase and ATP-dependent Ca++ uptake in the ER fraction. The molecular mechanism whereby specific trace elements Zn++, Cr++ and others antagonize Ca++ dependent insulin release from intact islets will be evaluated to determine if these cations mediate their effects at a subcellular level by interference with ATP-dependent Ca++ transport and ATPase activities in the ER fraction.